Frequently Asked Questions &
APFS Filesystem Secrets
Transparent explanations of macOS storage mechanics, Apple File System (APFS) behaviors, snapshots, and privacy protections.
In macOS APFS, multiple independent volumes share a single physical storage pool called the APFS Container. When DiskView scans your startup drive, it examines live files on the Data volume.
The physical container also houses hidden auxiliary system volumes:
- VM (`/System/Volumes/VM`): Dynamic virtual memory swap files (`swapfile0`, `swapfile1`) and sleep image (typically 5–15 GB).
- Preboot (`/System/Volumes/Preboot`): Apple Silicon kernel collections and cryptographic credentials (5–12 GB).
- Recovery: Bootable macOS Recovery partition (2–3 GB).
- Update: Staged macOS system upgrade installers.
These volumes occupy physical blocks in the container pool, but their contents are deliberately isolated from regular user file scans.
If Time Machine is enabled on your Mac, macOS automatically generates APFS Local Snapshots.
Because APFS uses Copy-on-Write (CoW), deleting a 20 GB file removes its directory entry from Finder, but the underlying data blocks remain physically retained on the SSD as part of the local snapshot until pruned.
macOS classifies these retained blocks as "Purgeable Space". The operating system will automatically free them whenever free storage drops below critical thresholds. You can inspect local snapshots in Terminal via:
Apple's modern FileProvider framework uses APFS Dataless Placeholder Files (flagged with SF_DATALESS in file system metadata).
To save SSD space, cloud storage providers keep unread files on remote cloud servers until you double-click them. Their physical disk allocation (st_blocks) on your Mac is literally 0 bytes, even though Finder displays their logical remote size (e.g., 500 MB).
DiskView prioritizes actual physical SSD consumption. Once you download an evicted file locally, DiskView will immediately reflect its true physical footprint.
When you duplicate a file in macOS Finder on an APFS volume, macOS creates an APFS Clone. Both directory entries point to the identical physical storage extents without consuming double the disk space.
DiskView lists both files in the treemap so you can manage and navigate them. However, deleting only one copy will not reclaim physical disk space; the storage is only returned to the free pool when all references to those data blocks are erased.
Virtual machine disk images and containers like Docker.raw are Sparse Files. A virtual disk might have a declared maximum limit of 1 TB, but only occupy 12 GB of real written blocks.
DiskView evaluates min(logicalSize, allocatedSize) to avoid misleading users with hundreds of gigabytes of unwritten, empty virtual space.
No. Absolutely none. DiskView does not include any analytics libraries, tracking pixels, advertising frameworks, or remote update pings.
It has zero outgoing network permissions and runs 100% locally on your machine. Your file names, folder hierarchies, and disk contents never leave your Mac.
DiskView runs on:
- macOS: macOS 14.0 Sonoma, macOS 15.0 Sequoia, or later.
- Hardware: Apple Silicon (M1, M2, M3, M4 series) and Intel 64-bit processors (Universal Binary).
- RAM: Less than 50 MB required during active operation.
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